Abstract. Whole cells of Desulfobulbus propionicus fermented[1-13 C]ethanol to [2-13 C] and [3 -13 C]propionate and [1-t 3 C]-acetate, which indicates the involvement of a randomizing pathway in the formation of propionate. Cell-free extracts prepared from cells grown on lactate (without sulfate) contained high activities of methylmalonyl-CoA:pyruvate transcarboxylase, NAD-dependent malate de_hydrogenase, fumarase, succinyl-CoA synthetase, propionate kinase, NAD(P)-independent pyruvate dehydrogenase, phosphotransacetylase, acetate kinase and reasonably high activities of NAD(P)-independent L(+)-lactate dehydrogenase, fumarate reductase and succinate dehydrogenase. Cell-free extracts catalyzed the conversion of succinate to propionate in the presence ofpyruvate, CoA and ATP and the oxaloacetare-dependent conversion of propionate to succinate. After growth on lactate or propionate in the presence of sulfate similar enzyme levels were found except for fumarate reductase which was considerably lower. Fermentative growth on lactate led to higher cytochrome b contents than growth with sulfate as electron acceptor.The labeling studies and the enzyme measurements demonstrate that in Desulfobulbus propionate is formed via a succinate pathway involving a transcarboxylase like in Propionibacterium. The same pathway may be used for the degradation of propionate to acetate in the presence of sulfate.
Abstract. Whole cells of Pelobacter propionicus fermented(1-13C) ethanol and CO2 to nearly equal amounts of (2-13C) and (3-13C) propionate and to (1-13C) acetate indicating a randomizing pathway of propionate formation. Enzymes involved in the fermentation were assayed in cell-free extracts and cetyltrimethylammonium bromide-permeabilized cells grown with ethanol as sole substrate. Alcohol dehydrogenase, aldehyde dehydrogenase (benzylviologen-reducing), phosphate acetyl transferase, acetate kinase, pyruvate synthase, methylmalonyl CoA: pyruvate transcarboxylase, propionyl CoA: succinate CoA transferase, and the enzymes of the succinate-methylmalonyl CoA pathway all were detected at activities sufficient to be involved in ethanol fermentation. Very low amounts of a b-type cytochrome were detected in ethanol-grown cells (46 nmol 9 g protein-1). Low cell yields obtained with ethanol as substrate indicate that P. propionicus does not conserve energy by electron transport-linked fumarate reduction. Despite the presence of a hydrogenase and a shift in the fermentation of lactate towards the formation of more propionate in the presence of hydrogen, P. propionicus was unable to catalyze the reduction of acetate and CO2 to propionate, unlike Desulfobulbus propionicus.
The degradation of [1‐14C]‐ and [2‐14C] propionate to acetate and bicarbonate by the sulfate‐ reducing bacterium Desulfobulbus propionicus was studied. When [1‐14C]propionate was used, more than 95% of the label was recovered in the HCO3− fraction. [2‐14C]Propionate was quantitatively converted into labeled acetate of which the methyl and carboxyl group were equally labeled. These results are in accordance with a randomizing route such as the methylmalonyl‐CoA pathway for propionate degradation and support earlier evidence for the functioning of this pathway on the basis of enzyme assays.
IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Document VersionPublisher's PDF, also known as Version of record Publication date: 1988 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Kremer, D. R., Veenhuis, M., Fauque, G., Peck Jr., H. D., LeGall, J., Lampreia, J., ... Hansen, T. A. (1988). Immunocytochemical localization of APS reductase and bisulfite reductase in three Desulfovibrio species. Archives of Microbiology, 150(3). https://doi.org/10.1007/BF00407795 Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. with APS reductase antibodies resulted in a distribution of gold particles over the cytoplasmic membrane region. The localization of the two enzymes is discussed with respect to the mechanism and energetics of dissimilatory sulfate reduction. Key words:Desulfovibrio -Dissimilatory sulfate reduction -APS reductase -Bisulfite reductase -Enzyme localization -Immunogold labeling Dissimilatory sulfate reduction is carried out by a large variety of bacteria (Hansen 1988;Widdel 1988). Most studies on its mechanism have been confined to bacteria belonging to the genus Desulfovibrio (Peck and LeGall 1982;LeGall and Fauque 1988). Dissimilatory sulfate reduction proceeds as follows:Sulfate is activated by ATP-sulfurylase to adenosine phosphosulfate (APS), which is subsequently reduced to sulfite plus AMP by the enzyme APS reductase (LeGall and Fauque 1988). In D. vulgaris Hildenborough APS reductase is a non-heme iron flavoprotein containing two different subunits, of 72 kD and 20 kD molecular mass, but it has an unknown subunit structure (Bramlett and Peck 1975). Its natural electron donor is not known. APS reductase has been detected in several genera of sulfate-reducing bacteria (Stille and Triiper 1984). Offprint requests to: T. A. HansenThe biochemistry of the reduction of sulfite to sulfide is somewhat controversial. A cyclic route, the so-called trithionate pathway, has been postulated, in which trithionate and thiosulfate are intermediates (Akagi 1981). In this route sulfite is first reduced to trithionate by the enzyme bisulfite reductase. However, strong indications were found that in Desulfovibrio spp. this is not the natural pathway (Chambers and Trudinger 1975;LeGall and Fauque 1988) and that in vivo a direct six electron reduction of sulfite to sulfide by the enzyme bisulfite reductase may occur. Whatever route is functioning, bisulfite reductase plays a key role in the dissimilatory reduction of sulfite. Four classes of bisulfite reductas...
The degradation of [1‐14C]‐ and [2‐14C] propionate to acetate and bicarbonate by the sulfate‐ reducing bacterium Desulfobulbus propionicus was studied. When [1‐14C]propionate was used, more than 95% of the label was recovered in the HCO3− fraction. [2‐14C]Propionate was quantitatively converted into labeled acetate of which the methyl and carboxyl group were equally labeled. These results are in accordance with a randomizing route such as the methylmalonyl‐CoA pathway for propionate degradation and support earlier evidence for the functioning of this pathway on the basis of enzyme assays.
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